Size greatly varies between species, from the dwarf crocodile to the saltwater crocodile. Species of Palaeosuchus and Osteolaemus grow to an adult size of just 1 metre (3.3 ft) to 1.5 metres (4.9 ft). Larger species can reach over 4.85 metres (15.9 ft) long and weigh well over 1,200 kilograms (2,600 lb). Crocodilians show pronounced sexual dimorphism with males growing much larger and more rapidly than females. Despite their large adult size, crocodiles start their life at around 20 centimetres (7.9 in) long. The largest species of crocodile is the saltwater crocodile, found in eastern India, northern Australia, throughout south-east Asia, and in the surrounding waters.
Two larger certifiable records are both of 6.2 metres (20 ft) crocodiles. The first crocodile was shot in the Mary River in the Northern Territory of Australia in 1974 by poachers and measured by wildlife rangers. The second crocodile was killed in 1983 in the Fly River, Papua New Guinea. In the case of the second crocodile it was actually the skin that was measured by zoologist Jerome Montague, and as skins are known to underestimate the size of the actual animal, it is possible this crocodile was at least another 10 cm longer.
The largest crocodile ever held in captivity is an Estuarine–Siamese hybrid named Yai (Thai: ใหญ่, meaning big) (born 10 June 1972) at the famous Samutprakarn Crocodile Farm and Zoo, Thailand. This animal measures 6 m (19.69 ft) (19 ft 8 in) in length and weighs 1114.27 kg.
The largest captive crocodile alive in the US is located in South Carolina. In June 2002, Alligator Adventure introduced Utan, born in 1964 in Thailand. At 20 feet (6.1 m) long and weighing in at more than a ton, "Utan", the largest crocodile to ever be exhibited in the United States, made his new home in Myrtle Beach.
Wildlife experts, however, argue that the largest crocodile so far found in the Bhitarkanika was almost 23 feet (7.0 m) long, which could be traced from the skull preserved by the Kanika Royal Family. The crocodile was shot near Dhamara in 1926 and later its skull was preserved by the then Kanika King. Crocodile experts estimate the animal was between 20 feet (6.1 m) and 23 feet (7.0 m) long, as the size of the skull was measured one ninth of the total length of the body.
There is no reliable way of measuring crocodile age, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons. Bearing these inaccuracies in mind, the oldest crocodilians appear to be the largest species. C. porosus is estimated to live around 70 years on average, and there is limited evidence that some individuals may exceed 100 years. One of the oldest crocodiles recorded died in a zoo in Russia. A male freshwater crocodile at the Australia Zoo is estimated to be 130 years old. He was rescued from the wild by Bob Irwin and Steve Irwin after being shot twice by hunters. As a result of the shootings, this crocodile (known affectionately as "Mr. Freshy") has lost his right eye.
Crocodiles have smooth skin on their belly and side, while their dorsal surface is armoured with large osteoderms. The armoured skin has scales and is thick and rugged, providing some protection. They are still able to absorb heat through this thick, rugged armour as a network of small capillaries push blood through the scales to absorb heat.